1. Field of the Invention
The present invention relates to an apparatus for processing a photosensitive material in which a photosensitive material such as a printing plate is processed using a processing liquid such as a developer. The present invention also relates to an area measurement method for measuring the area of a photosensitive material.
2. Description of the Background Art
An apparatus for processing a photosensitive material has been in practical use in which a photosensitive material is processed while being carried along a predetermined transport path. As an example, a dip-type apparatus for processing a photosensitive material is publicly known that processes a photosensitive material dipped in a processing tank storing a processing liquid. Such a dip-type processing apparatus is provided with a replenishment mechanism that adds a replenisher to a processing liquid in the processing tank in response to the process upon the photosensitive material. The addition of the replenisher is intended to compensate for the reduction of the degree of activity of the processing liquid.
In some cases, the replenishment mechanism measures the area of the photosensitive material and then adds the replenisher in an amount responsive to the measured area. The replenishment mechanism operating in this manner has a plurality of photosensitive material detectors for measuring the area of the photosensitive material arranged across the width of the photosensitive material. As an example, the photosensitive material detectors are photoelectric sensors or mechanical microswitches provided near the entrance of the processing apparatus. The photosensitive material detectors each detect the presence or absence of the photosensitive material directly thereover or thereunder.
FIG. 5 shows the arrangement of photosensitive material detectors in a conventional apparatus for processing a photosensitive material. A photosensitive material is carried in a direction indicated by an arrow A in FIG. 5. A plurality of photosensitive material detectors are arranged in a row in a direction B perpendicular to the direction A, in a symmetrical manner about a line L as the center line of the width of a transport path of a photosensitive material. Photosensitive material detectors arranged on one of sides with respect to the center line L (the right-hand side of FIG. 5) are identified as 114a, 114b, 114c and 114d in this order when viewed from the center line L. Photosensitive material detectors arranged on the other side (the left-hand side of FIG. 5) are identified as 114a′, 114b′, 114c′ and 114d′ in this order when viewed from the center line L.
A photosensitive material with every width is carried, with its center of the width coinciding with the center line L of the transport path. Thus in this processing apparatus, four different widths of a photosensitive material can be identified. More specifically, of a first range of less than a distance d1 between the photosensitive material detectors 144a and 144a′, a second range of not less than the distance d1 and less than a distance d2 between the photosensitive material detectors 144b and 144b′, a third range of not less than the distance d2 and less than a distance d3 between the photosensitive material detectors 144c and 144c′, and a fourth range of not less than the distance d3 and less than a distance d4 between the photosensitive material detectors 144d and 144d′, it is determined which of the first, second, third and fourth ranges the width of a photosensitive material has.
In order to improve timing accuracy in adding a replenisher to a processing liquid in a processing tank, the width of a photosensitive material is desirably measured at increased resolution. This may be realized by the less space between photosensitive material detectors. However, due to restriction imposed by the size of photosensitive material detectors itself, these detectors cannot be densely arranged in some cases.
Japanese Patent Application Laid-Open No. 2001-100432 introduces an exemplary apparatus for processing a photosensitive material provided with detectors for measuring the width of a photosensitive material. However, this apparatus suffers from a different problem that the measured widths contain a considerably high degree of inaccuracy when a photosensitive material deviates from the center of the transport path while being carried.